Communication device, a method of operating a communication device and a communication system

ABSTRACT

A mobile station ( 100 ) in a mobile communication system obeys commands received from a serving base station ( 300 ) to decrease its transmission rate, and obeys commands received from the serving base station ( 300 ) to increase its transmission rate except when a predetermined time period is in progress. It obeys commands received from a non-serving base station ( 200, 400 ) to decrease its transmission rate, it initiates the predetermined time period in response to receiving such commands, and it terminates the predetermined time period in response to a further command from the same non-serving base station ( 200, 400 ).

The invention relates to a communication device, to a method ofoperating a communication device, and to a communication systemcomprising a communication device. The invention has application in,particularly but not exclusively, mobile communication devices andsystems such as the Universal Mobile Telecommunication System (UMTS).

According to current proposals for the UMTS Enhanced Uplink, “serving”and “non-serving” base stations (BSs) can adjust the transmission rategranted to a mobile station (MS) by transmitting the following commandsto the MS. “−1” commands take precedence over other commands.

Serving BS: “Increase rate” (+1)

-   -   “Decrease rate” (−1) or    -   “Keep current rate” (DTX)        Non-serving BS: “Decrease rate” (−1) or    -   “Don't care” (DTX)        where “DTX” represents no transmission.

By “serving” base station we mean a BS which is configured to receivetransmissions from a particular MS and by “non-serving” base station wemean a BS which may receive transmissions from the MS but is notrequired to do so. Typically a serving BS has greater control than anon-serving BS over the transmission parameters used by the MS,resulting in typically more reliable reception of MS transmissions byserving BSs than by non-serving BSs. Typically each MS is associatedwith exactly one serving BS, and may simultaneously be associated with aplurality of non-serving BSs.

The non-serving BSs are not permitted to transmit the +1 signal, as onlythe serving BS has the authority to give a MS permission to increase itstransmission rate.

One problem which can occur with this scheme is that the serving andnon-serving BSs can cause the granted transmission rate to togglebetween two values if a non-serving BS transmits −1, followed by DTXonce the MS's transmitted rate is down to an acceptable level, while theserving BS can tolerate a higher rate, which requires a higher receivedpower level, and transmits +1 continually. A further problem with thistoggling is the frequent signalling from non-serving BSs, which wastesdownlink (BS to MS) resources and causes more interference to otherusers.

One way to overcome the toggling is for all the non-serving BSs totransmit “−1” continually until the MS transmission rate is well belowits acceptable level. However, this does not solve the problem of thelarge quantity of downlink signalling, and also results in a lowertransmission rate from the MS than should in fact be possible.

It is also known to include a hysteresis period, such that the MS willignore “+1” commands from the serving BS until the expiry of apredetermined time period after the most recent “−1” command wasreceived from any of the non-serving BSs. Such a scheme is illustratedin FIG. 1. FIG. 1, graph (a) shows a sequence of “+1” commands 110transmitted by a serving BS at intervals of one transmission timeinterval (TTI). Graph (c) shows the transmission rate being increased bythe MS from rate R1 to rate R2 in response to the “+1” commandtransmitted at time t=0. Graph (b) shows a “−1” command 120 transmittedby a non-serving BS at time t=1, and in response to this in graph (c)the transmission rate is decreased. A hysteresis period T commencesafter the receipt of the “−1” command for a predetermined period of fourTTIs, such that the next three “+1” commands from the serving BS areignored. The length of the predetermined time period is a trade-offbetween reducing downlink signalling from the non-serving BSs, whichimplies using a long period, and maximising the possible transmissionrate for the MS, which implies using a short period. Thus the use of ahysteresis period in this way will result in the granted rate for the MSbeing lower than necessary if the situation of the non-serving BSschanges before the end of the hysteresis period such that they cantolerate a higher transmission rate from the MS.

An object of the invention is to provide improved control of atransmission parameter.

According to a first aspect of the invention there is provided a methodof operating a first communication device in a communication systemcomprising a plurality of stations, the method comprising:

-   -   in response to receiving a first command from a first station,        decreasing a parameter value and commencing the timing of a        first predetermined time period;    -   in response to receiving a second command from the first        station, terminating the timing of the first predetermined time        period if the timing is in progress;    -   in response to receiving a first command from a second station,        decreasing the parameter value; and    -   in response to receiving a second command from the second        station, increasing the parameter value unless the timing of the        first predetermined time period is in progress.

According to a second aspect of the invention there is provided acommunication device comprising:

-   means for receiving commands from a plurality of stations;-   adjustment means for adjusting a parameter value in response to the    received commands; and-   timing means for timing one or more predetermined time periods;    wherein    -   in response to the receipt of a first command from a first        station, the adjustment means is adapted to decrease the        parameter value and the timing means is adapted to commence the        timing of a first predetermined time period;    -   in response to the receipt of a second command from the first        station, the timing means is adapted to terminate the timing of        the first predetermined time period;    -   in response to the receipt of a first command from a second        station, the adjustment means is adapted to decrease the        parameter value; and    -   in response to the receipt of a second command from the second        station, the adjustment means is adapted to increase the        parameter value unless the timing of the first predetermined        time period by the timing means is in progress.

According to a third aspect of the invention there is provided acommunication system comprising a communication device according to thesecond aspect of the invention.

The invention provides a way of enhancing the known transmission ratecontrol scheme described above which uses a hysteresis period, byproviding a way for terminating the hysteresis period prior to itsexpiry in response to a command from the same station that caused theinitiation of the hysteresis period. The invention enables the togglingof the granted transmission rate to be avoided without requiring thenon-serving BSs to send repeated “−1” commands, as well as enabling thenon-serving BSs to terminate the hysteresis period to allow the servingBS to increase the rate, for example if the interference level of thenon-serving BSs changes so they can tolerate a higher transmission ratefrom the MS. Other transmission parameters may be controlled using theinvention, instead of or in addition to the transmission rate.

The invention will now be described, by way of example only, withreference to the accompanying drawings wherein:

FIG. 1 is a timing diagram illustrating a prior art method;

FIG. 2 is a timing diagram illustrating a first example of theinvention;

FIG. 3 is a timing diagram illustrating a second example of theinvention;

FIG. 4 is a block schematic diagram of a communication system; and

FIG. 5 illustrates an embodiment of a method.

According to the invention, a command from a non-serving BS is definedto provide a way for a non-serving BS to terminate a hysteresis periodthat was initiated by a command that it transmitted. Conveniently, a“+1” command may serve this purpose, terminating a hysteresis periodthat was initiated by a “−1” command. An example of a set of commandstransmitted by a non-serving base station, and their significance to aMS, is shown in Table 1.

TABLE 1 Significance outside Significance within Command hysteresisperiod hysteresis period −1 Decrease rate Decrease rate DTX Don't care -can Keep current rate, increase rate if permitted unless commanded to byserving BS decrease by serving BS +1 Not applicable Don't care - canincrease rate if permitted by serving BS

The “+1” command is not applicable outside of a hysteresis periodbecause such a command will not generally be transmitted by anon-serving bases station; if it were to be transmitted it would beignored by the MS.

FIGS. 2 and 3 illustrate two examples of the operation of the invention.In both FIGS. 2 and 3, graph (a) shows “+1” commands 110 transmitted bya serving BS at intervals of time t corresponding to one TransmissionTime Interval (TTI), which is the interval at which Protocol Data Units(PDUs) are transferred between the physical layer and the MAC layer ofthe protocol stack in UMTS. The time may alternatively be quantified inother units, such as radio frames, hybrid ARQ process periods, seconds,or timeslots.

In FIG. 2, graph (c) shows the transmission rate being increased by theMS from rate R1 to rate R2 in response to the “+1” command 110transmitted by the serving BS at time t=0. Graph (b) shows a “−1”command 120 transmitted by a non-serving BS at time t=1, and in responseto this in graph (c) the transmission rate is decreased from rate R2 torate R1. A hysteresis period T commences after the receipt of the “−1”command for a predetermined period of four TTIs. The “+1” commandtransmitted by the serving BS at time t=2 is ignored, so thetransmission rate is maintained at R1. At time t=3 the non-serving BStransmits a “+1” command 130, for example because interference at thatnon-serving BS reduces, which has the effect of terminating thehysteresis period, thus permitting the MS to increase the transmissionrate in response to receiving the “+1” command transmitted by theserving BS at time t=3, and thereafter in response to the subsequent“+1” commands transmitted by the serving BS.

Note that a hysteresis period is not terminated by a command from adifferent non-serving station, i.e. a different non-serving station thanthe one that initiated the hysteresis period.

Hysteresis periods initiated by different non-serving base stations mayoverlap, and the MS ignores “+1” commands received while any hysteresisperiod is in progress. An example of this situation is illustrated inFIG. 3.

In FIG. 3, graph (d) shows the transmission rate being increased by theMS from rate R2 to rate R3 in response to the “+1” command 110transmitted by the serving BS at time t=0. Graph (c) shows a “−1”command 120 transmitted by a first non-serving BS at time t=1, and inresponse to this in graph (d) the transmission rate is decreased fromrate R3 to rate R2 and a first hysteresis period T_(c) commences afterthe receipt of this “−1” command 120 for a predetermined period of threeTTIs. The “+1” command transmitted by the serving BS at time t=2 isignored because the hysteresis period T_(c) is in progress.

Graph (b) of FIG. 3 shows at time t=2 a second non-serving BStransmitting a “−1” command 120 and the MS reduces the transmission ratefrom R2 to R1 in response to receiving this command and also commences asecond hysteresis period T_(b) for a predetermined period of three TTIs.

In graph (c) of FIG. 3, at time t=3 the first non-serving BS transmits a“+1” command 130, for example because interference at that non-servingBS reduces, which has the effect of terminating the first hysteresisperiod T_(c), but not the second hysteresis period T_(b). Because thesecond hysteresis period T_(b) is still in progress, the MS does notincrease the transmission rate in response to receiving the “+1”commands transmitted by the serving BS at times t=3 or 4, but the MS ispermitted to increase the transmission rate in response to receiving the“+1” command transmitted by the serving BS at time t=5 because thesecond hysteresis period T_(b) expires after that command.

Alternatively, the MS may not resume obeying “+1” commands transmittedby the serving BS until such a command is received whilst no hysteresisperiod is in progress.

In some embodiments of the invention, any rate change at the end of thehysteresis period, either when the predetermined time period expires orwhen it is terminated by the non-serving BSs, may be of a magnitudedifferent from the most recent “rate increase” command received from theserving BS; for example, the rate change may be the sum of the ratechange commands received from one or more BSs during the hysteresisperiod.

The up or down commands may be single bits, or may take a range ofdifferent values signifying for example the magnitude of the desiredtransmission rate change. The representation of commands transmitted bythe serving and non-serving base stations need not be identical.

FIG. 4 illustrates a block schematic diagram of a communication systemcomprising a first communication device 100, for example an MS, andthree communication stations 200, 300 and 400, for example BSs, of whichone (300) is a serving station and the other two (200, 400) arenon-serving stations. The communication device 100 comprises atransmitter (Tx) 10 and receiver (Rx) 20 for communication with thecommunication stations 200, 300, 400, a processing means 30, such as aprocessor, coupled to the transmitter 10 and receiver 20 for generatingsignals for transmission and for processing received commands,adjustment means 40 coupled to the processing means 30 for adjusting, inresponse to received commands and in accordance with the methoddescribed, a parameter value, such as transmission rate, of signalsgenerated by the processing means 30, and a timing means 50 coupled tothe processing means 30 for timing the one or more predetermined timeperiods. Although the examples of FIGS. 2 and 3 have been described byreference to two predetermined hysteresis periods T_(b) and T_(c), thetiming may be implemented using a single timer that is restarted at thecommencement of each predetermined time period. Either or both of theadjustment means 40 and the timing means 50 may be implemented in ageneral purpose computer or using customised circuitry.

FIG. 5 illustrates an embodiment of a method 500 of operating a firstcommunication device in a communication system comprising a plurality ofstations. At act 502, in response to receiving a first command from afirst station, the first communication device decreases a parametervalue and commence the timing of a first predetermined time period. Atact 504, in response to receiving a second command from the firststation, the first communication device terminates the timing of thefirst predetermined time period if the timing is in progress. At act506, in response to receiving a first command from a second station, thefirst communication device decreases the parameter value. At act 508, inresponse to receiving a second command from the second station, thefirst communication device increases the parameter value unless thetiming of the first predetermined time period is in progress. At act510, in response to receiving a first command from a third station, thefirst communication device decreases a parameter value and commences thetiming of a second predetermined time period. At act 512, in response toreceiving a second command from the third station, the firstcommunication device terminates the timing of the second predeterminedtime period if the timing of the second predetermined time period is inprogress. At act 514, in response to receiving the second command fromthe second station, the first communication device increases theparameter value unless the timing of at least one of the first andsecond predetermined time period is in progress.

Although the invention has been described with reference to commands foradjusting the transmission rate, the invention is also applicable to theadjustment of other parameters, such as transmit power, modulationscheme, number of transmitted carrier frequencies, number of transmittedtimeslots, number of transmitted spreading codes, spreading factor orcode rate (e.g. the ratio of information bits to redundancy bits).

In the claims, the first and third stations may be non-serving stationsand the second station may be a serving station.

Although the invention has been described with reference to UMTS, it isapplicable to other types of mobile communication system and devices.

In the present specification and claims the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof other elements or steps than those listed. The inclusion of referencesigns in parentheses in the claims is intended to aid understanding andis not intended to be limiting.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the art of mobilecommunications and which may be used instead of or in addition tofeatures already described herein.

1. A method of operating a first communication device in a communicationsystem comprising a plurality of stations, the method being performedusing the first communication device and comprising: in response toreceiving a first command from a first station, decreasing a parametervalue and commencing the timing of a first predetermined time period; inresponse to receiving a second command from the first station,terminating the timing of the first predetermined time period if thetiming is in progress; in response to receiving a first command from asecond station, decreasing the parameter value; and in response toreceiving a second command from the second station, increasing theparameter value unless the timing of the first predetermined time periodis in progress.
 2. The method as claimed in claim 1, further comprising:in response to receiving a first command from a third station,decreasing a parameter value and commencing the timing of a secondpredetermined time period; in response to receiving a second commandfrom the third station, terminating the timing of the secondpredetermined time period if the timing of the second predetermined timeperiod is in progress; and in response to receiving the second commandfrom the second station, increasing the parameter value unless thetiming of at least one of the first and second predetermined time periodis in progress.
 3. The method as claimed in claim 1 wherein theincreasing and decreasing of the parameter value is indicative of anadjustment of at least one of: transmission rate; transmit power;modulation scheme; number of transmitted carrier frequencies; number oftransmitted time slots; number of transmitted spreading codes; spreadingfactor; and code rate.
 4. A communication device comprising: means forreceiving commands from a plurality of stations; adjustment means foradjusting a parameter value in response to the receiving commands; andtiming means for timing one or more predetermined time periods; whereinin response to the receipt of a first command from a first station, theadjustment means is configured to decrease the parameter value and thetiming means is configured to commence the timing of a firstpredetermined time period; in response to the receipt of a secondcommand from the first station, the timing means is configured toterminate the timing of the first predetermined time period; in responseto the receipt of a first command from a second station, the adjustmentmeans is configured to decrease the parameter value; and in response tothe receipt of a second command from the second station, the adjustmentmeans is configured to increase the parameter value unless the timing ofthe first predetermined time period by the timing means is in progress.5. The communication device as claimed in claim 4 wherein in response tothe receipt of a first command from a third station, the adjustmentmeans is configured to decrease the parameter value and the timing meansis configured to commence the timing of a second predetermined timeperiod; in response to the receipt of a second command from the thirdstation, the timing means is configured to terminate the timing of thesecond predetermined time period; and in response to the receipt of thesecond command from the second station, the adjustment means isconfigured to increase the parameter value unless the timing of at leastone of the first and second predetermined time periods by the timingmeans is in progress.
 6. The communication device as claimed in claim 4wherein the increase and decrease of the parameter value is indicativeof an adjustment of at least one of: transmission rate; transmit power;modulation scheme; number of transmitted carrier frequencies; number oftransmitted time slots; number of transmitted spreading codes; spreadingfactor; and code rate.
 7. A communication system comprising: acommunication device having: means for receiving commands from aplurality of stations; adjustment means for adjusting a parameter valuein response to the receiving commands; and timing means for timing oneor more predetermined time periods; wherein in response to the receiptof a first command from a first station, the adjustment means isconfigured to decrease the parameter value and the timing means isconfigured to commence the timing of a first predetermined time period;in response to the receipt of a second command from the first station,the timing means is configured to terminate the timing of the firstpredetermined time period; in response to the receipt of a first commandfrom a second station, the adjustment means is configured to decreasethe parameter value; and in response to the receipt of a second commandfrom the second station, the adjustment means is configured to increasethe parameter value unless the timing of the first predetermined timeperiod by the timing means is in progress; and a plurality of stationsfor communicating with the communication device.
 8. The communicationsystem of claim 7 wherein in response to the receipt of a first commandfrom a third station, the adjustment means is configured to decrease theparameter value and the timing means is configured to commence thetiming of a second predetermined time period; in response to the receiptof a second command from the third station, the timing means isconfigured to terminate the timing of the second predetermined timeperiod; and in response to the receipt of the second command from thesecond station, the adjustment means is configured to increase theparameter value unless the timing of at least one of the first andsecond predetermined time periods by the timing means is in progress. 9.The communication system of claim 7 wherein the increase and decrease ofthe parameter value is indicative of an adjustment of at least one of:transmission rate; transmit power; modulation scheme; number oftransmitted carrier frequencies; number of transmitted time slots;number of transmitted spreading codes; spreading factor; and code rate.